1. Field of the Invention
The present invention relates to a data transmitter. More particularly, the present invention relates to a differential transmitter and an auto-adjustment method of data strobe thereof.
2. Description of Related Art
A differential transmitter can convert an input signal into a differential signal, and transmit the differential signal to a next stage (receiver). Taking a low voltage differential signal (referred to as LVDS hereinafter) as an example, all present LVDS transmitters have two methods for input data strobe, one is to latch an input data signal Din at a rising edge of a clock signal CLK (as shown in FIG. 1A), the other is to latch the input data signal Din at a falling edge of the clock signal CLK (as shown in FIG. 1B).
The conventional LVDS transmitter has a input mode control terminal RFB for determining whether the input data signal Din is latched at the rising edge (FIG. 1A) or at the falling edge (FIG. 1B) of the clock signal CLK. A user (system designer) has to set a correct input data strobe method for the LVDS transmitter via the input mode control terminal RFB of the LVDS transmitter.
FIG. 2 is a block diagram illustrating a conventional LVDS transmitter 200. By pull-up or pull-down the input mode control terminal RFB of the transmitter 200 via an external circuit, the user (system designer) may correctly set the input data strobe method for the transmitter 200. The conventional LVDS transmitter 200 has a multiplexer 210. Under control of the input mode control terminal RFB, the multiplexer 210 determines to switch the clock signal CLK and the data signal Din to a rising edge strobe unit 220 or switch the clock signal CLK and the data signal Din to a falling edge strobe unit 230. If the multiplexer 210 switches the clock signal CLK and the data signal Din to the rising edge strobe unit 220, the rising edge strobe unit 220 then latches the data signal Din at the rising edge of the clock signal CLK, and converts a latching result thereof to be a first differential output signal. If the multiplexer 210 switches the clock signal CLK and the data signal Din to the falling edge strobe unit 230, the falling edge strobe unit 230 then latches the data signal Din at the falling edge of the clock signal CLK, and converts a latching result thereof to be a second differential output signal.
When the input mode control terminal RFB of the transmitter 200 is pulled up via the external circuit, the multiplexer 210 switches the clock signal CLK and the data signal Din to the rising edge strobe unit 220, so that the input data signal Din is latched at the rising edge of the clock signal CLK. When the input mode control terminal RFB is pulled down, the multiplexer 210 switches the clock signal CLK and the data signal Din to the falling edge strobe unit 230, so that the input data signal Din is latched at the falling edge of the clock signal CLK.
Therefore, the user (system designer) has to know in advance whether or not the input data signal Din belongs to a type shown in FIG. 1A or belonged to a type shown in FIG. 1B, so as to pull up or pull down the input mode control terminal RFB. However, errors of data strobe occurred due to improper setting by the user (system designer) cannot be avoided.